Batteries such as alkaline storage batteries and lithium ion secondary batteries are widely used as the power source for portable devices, machine tools, or electric vehicles. Of these, nickel metal-hydride storage batteries have a relatively high energy density and excellent durability, and the applications thereof, including as power sources for electric vehicles, are being expanded.
Generally, the main components of nickel metal-hydride storage batteries include: a positive electrode formed by filling a three-dimensional metal porous material with nickel hydroxide and other materials; and a negative electrode formed by applying an electrode mixture paste composed of a hydrogen-absorption alloy and other materials to porous metal thin plate (hereinafter simply abbreviated as a “core material”) such as a punched metal. Of these two, the negative electrode can be produced continuously because of the nature of its production process, which has received attention as a highly efficient process. Specifically, a method has been proposed in which, after the core material is immersed in the electrode mixture paste, the application amount of the electrode mixture paste is adjusted to produce a paste-coated sheet.
For example, a mixture paste of a negative electrode for nickel metal-hydride storage batteries contains a hydrogen-absorption alloy having a high specific gravity of approximately 8 g/ml. Therefore, in this case, the hydrogen-absorption alloy sediments over time. As the sedimentation proceeds, only the supernatant of the electrode mixture paste is applied to a core material. Therefore, the composition of the applied material is not uniform, and at the same time the application amount decreases over time. In order to avoid this, for example, the following methods have been proposed: a method in which a kneaded paste is left to stand for a predetermined period of time to temporarily increase the viscosity and thereafter is kneaded again (for example, Patent Document 1); a method in which a paste is stirred at a constant temperature and thereafter is subjected to aging in a stored state (for example, Patent Document 2); and a method in which a paste bath having a stirring function is provided at a area adjacent to an application position (for example, Patent Document 3). In addition to these, it may be effective to evolve, for example, the following methods, although these are examples for other battery systems: a method in which stirring means is provided right at an application position (for example, Patent Documents 4 and 5); and a method in which a paste is ultrasonically dispersed while being circulated (for example, Patent Document 6).    [Patent Document 1] Japanese Patent Laid-Open Publication No. 9-204917    [Patent Document 2] Japanese Patent Laid-Open Publication No. 9-035709    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2000-323138    [Patent Document 4] Japanese Patent Laid-Open Publication No. 2000-243384    [Patent Document 5] Japanese Patent Laid-Open Publication No. 2001-076708    [Patent Document 6] Japanese Patent Laid-Open Publication No. 10-223217